1. Field of the Invention
The invention relates to semiconductor integrated circuit devices, and more particularly to large area transistors.
2. Related Art
A die (also called chip) is a small piece of silicon wafer, bounded by adjacent scribe lines in the horizontal and vertical directions, that contains the complete device being manufactured. An integrated circuit (also called an IC) comprises many interconnected circuit elements on a single die. Such interconnected circuit elements typically include semiconductor devices, such as transistors or diodes, and other devices, such as capacitors, resistors, and the like. Interconnects (also called wiring) are highly conductive material, usually aluminum, polycrystalline silicon (polysilicon), copper, or the like, that carry electrical signals to different parts of a die.
Signals generated on chip must be sent off chip in order to be coupled to other IC's or components. A common type of transistor used in IC's is a metal-oxide-silicon (MOS) field effect transistor (FET). Complementary metal-oxide-silicon (CMOS) transistor technology includes both p-type and n-type conductivity MOS transistors. Because today's IC's comprise millions of transistors, any one transistor is too small to output sufficient current to “drive” an off-chip (i.e., some other off-chip IC or component) or on-chip load.
So called “large driver” transistors comprise many MOS transistors connected together to provide sufficient output current to drive an off-chip or on-chip load. These drivers usually carry large current. Of course, larger current (I) means a larger voltage (V) drop (i.e., V=I*R; where R=resistance), and more power (P) dissipation (i.e., P=I2*R) across devices and/or interconnects. Larger voltage drop means smaller voltage swing available at the output. More power dissipation means lower efficiency as more power is lost due to heat, etc. Accordingly, larger voltage drop and/or more power dissipation lead to poor circuit performance.
Thus, what is desired is a transistor layout design with low ohmic characteristics.